Elevated working platforms have long been utilized in the construction and maintenance of building walls. In general, such equipment is either ground supported or suspended from upper portions of the building. An example of a ground supported elevated working platform is described in U.S. Pat. No. 4,427,093, while a ground supported and power operated mobile working platform is disclosed in U.S. Pat. No. 3,817,346. Examples of the suspended version are depicted and described in U.S. Pat. Nos. 4,454,928; 4,453,619; and 4,074,789.
Although various types of equipment have been devised to safely support workers and equipment at the elevated heights required to perform such duties, probably the most commonly used equipment is portable scaffolding. Such scaffolding may be easily and quickly assembled at the jobsite, and may then be disassembled and reassembled at a new location at the jobsite. Sections of scaffold may be added or removed to selectively raise or lower the height of the working platform. Such scaffolding is easily disassembled, transported, and stored by most companies involved in providing elevated working platforms or services connected therewith.
In many installations, the assembled scaffolding is not intended to be moved about at a jobsite. A new construction, for instance, the ground adjacent the building walls may be very uneven, and scaffolding would generally be disassembled and reassembled at a new location at such a jobsite rather than attempting to move the assembled scaffolding as a unit. In other instances, such as those commonly associated with construction jobs wherein the ground adjacent the building is substantially level and perhaps paved or in building maintenance operations, assembled scaffolding is frequently moved as a unit. Such scaffolding is customarily provided with a plurality of rollers for easily moving the assembled scaffolding to the desired location, and is referred to as rolling scaffolding on a rolling tower.
When such rolling scaffolding is moved, personnel and/or heavy equipment are not intended to remain on the scaffolding for safety reasons. Care is therefore exercised in the industry to remind personnel of the dangers associated with moving scaffolding with men and/or equipment on the scaffold. Danger to personnel obviously involves the likelihood of personnel falling from the scaffolding. Also, the scaffolding may tip while being moved since it is "top heavy" with men or equipment. Equipment may fall from a scaffolding as it is being moved, which may injure people on the ground who are manually moving the scaffolding. Also, top heavy scaffolding with such equipment may tip or fall on people, or fall into the building wall, perhaps breaking glass or causing serious bodily injury. Nevertheless, the fact remains that people do not always heed safety instructions, and unfortunately people are injured by improperly moving rolling scaffolding.
Another problem associated with scaffolding and, in particular, rolling scaffolding, is that such equipment may be used although it has been improperly and unsafely assembled. Often, the people using the scaffolding are not the same people who erected the scaffolding. If, based upon a reasonably quick visual inspection, the user does not detect that the scaffolding or scaffolding base is improperly assembled, the scaffolding may be used and the error detected only after a fall and serious injury. Partially because of this reason, scaffolding bases of a substantially one-piece welded construction have been devised. Unfortunately, such a unitary scaffolding base cannot be easily transported between jobsites, and such a unitary base with a damaged component may be used in the field since the component cannot be easily and quickly repaired or replaced.
Many scaffolding bases are little more than four rollers attached to the bottom of conventional scaffolding legs. In field operations, the scaffolding legs tend to become bent when the scaffold is forced against a stationary object, thereby making the rolling tower unsafe. Also, the center of gravity of the rolling tower is rather high, since the legs of the scaffold may fit onto a "base" two feet or more above the ground.
In an effort to improve scaffolding safety, some manufacturers have provided rolling scaffolding bases with scaffolding base outriggers. Outriggers are intended to minimize the likelihood of scaffolding tipping while in use by extending ground supporting members outwardly from the conventional base roller position. Examples of these outriggers are shown in U.S. Pat. Nos. 4,397,373 and 4,427,093. According to the teachings of U.S. Pat. No. 4,194,591, scaffolding outriggers are used in a manner which prevents the rollers or casters from contacting the ground when the scaffolding is in use. Further examples of rolling scaffolding with outriggers are shown on pages 24-26 of a brochure entitled "Safway Scaffolds Company of Houston", dated 1981.
Rolling scaffolding base outriggers may increase scaffolding safety. Nevertheless, scaffolding with such outriggers still may present an unsafe condition, primarily because outriggers are not always properly utilized in field operations. Since outriggers extend outwardly from the base, the base may not be able to be moved as closely adjacent the building wall as the user desires. The user therefore has to elect either to not use that scaffolding, or to utilize that scaffolding by either cutting off the outriggers or otherwise utilizing the outriggers in a manner not intended by the manufacturer. Outriggers which may be moved into position with respect to the base may not be utilized if the user believes, although erroneously, that the outriggers are unnecessary. On the other hand, outriggers rigidly secured to the base may be cut from the base in order to render the scaffolding usable in certain situations. Moreover, outriggers rigidly secured to the base make transportation of the base much more difficult, and for that reason are not favored.
The disadvantages of the prior art are overcome by the present invention, and an improved rolling scaffolding base and mobile tower are hereinafter described.